Some selected highlights

The T Tauri phase of evolution occurs early in a star's lifetime, within ~10 Myrs of
its birth when it still retains a dense, dust and gas-rich circumstellar disk.
It is generally agreed that at least giant planet formation occurs during this phase,
terminating when the gas dissipates to leave a dusty debris disk. The properties of
the resultant planets are likely to depend strongly on the properties of the
dust within the circumstellar disk. This program aims to combine coronagraphy with
the polarimetric capabilities of NICMOS, HST's near-infrared camera, to study the
size distribution of dust particles within the disks surrounding a representative
sample of young stellar objects. The forthcoming set of observations will target GM Aurigae,
a ~0.8 solar-mass star with an age between 2 and 10 million years that has a substantial
circumstellar disk. Multiwavelength measurements strongly suggest that the disk, which likely
has a full diameter of ~600 AU, has a central gap, radius ~4 AU; that gap may well have been
cleared by a jovian-mass planet.

GO 11082: NICMOS Imaging of GOODS: Probing the Evolution of the Earliest Massive Galaxies,
Galaxies Beyond Reionization, and the High Redshift Observational Universe

GO 11178: Probing Solar System History with Orbits, Masses, and Colors of Transneptunian Binaries

Preliminary orbital determination for the KBO WW31, based on
C. Veillet's
analysis of CFHT observations; the linked image shows the improved orbital
derivation, following the addition of HST imaging

The Kuiper Belt consists of icy planetoids that orbit the Sun within a broad band
stretching from Neptune's orbit (~30 AU) to distance sof ~50 AU from the Sun
(see David Jewitt's Kuiper
Belt page for details). Over 500 KBOs (or trans-Neptunian objects, TNOs)
are currently known out of a population of
perhaps 70,000 objects with diameters exceeding 100 km. Approximately 2% of the known
KBOs are binary (including Pluto, one of the largest known KBOs, regardless of
whether one considers it a planet or not). This is a surprisingly high fraction, given
the difficulties involved in forming such systems and the relative ease with which
they can be disrupted. It remains unclear whether these systems formed from single
KBOs (through collisions or 3-body interactions) as the Kuiper Belt and
the Solar System have evolved,
or whether they represent the final tail of an initial (much larger) population of
primordial binaries. These issues can be addressed, at least in part, through deriving a
better understanding of the composition of KBOs - and those properties can be
deduced by measuring the orbital parameters for binary systems. The present proposal
will use the Planetary camera on WFPC2 to determine the relative orbits for several known KBO binaries.
Just as with binary stars,
the orbital period and semi-major axis give the total system mass, while the
mid-infrared properties (measured by Spitzer) allow an assessment of the surface area/diameters;
combining these measurements gives an estimate of the mean density.

Gravitational lensing is a consequence the theory of general relativity. Its importance
as an astrophysical tool first became apparent with the realisation (in 1979) that
the quasar pair Q0957+561 actually comprised two lensed images of the same
background quasar. In the succeeding years, lensing has been used primarily to probe the
mass distribution of galaxy clusters, using theoretical models to
analyse the arcs and arclets that are produced by strong lensing of background galaxies,
and the large-scale mass distribution, through analysis of weak lensing effects on
galaxy morphologies. Gravitational lensing can also be used to investigate the
mass distribution of individual galaxies. Until recently, the most common
background sources were quasars. Galaxy-galaxy lenses, however, offer a distinct advantage,
since the background source is extended, and therefore imposes a stronger constraints
on the mass distribution of the lensing galaxy than a point-source QSO. The
CFHT Legacy survey provides a powerful tool for identifying candidate galaxy-galaxy lenses.
Optical ground-based imaging, even from Hawaii, cannot match the results from a 2.4-metre
telescope in orbit. Thus, the
present program is using WFPC2 imaging to verify the nature of those candidates. The
high resolution images can then be analysed to model the underlying mass distribution.